Cold Forming Fasteners: What It Is, How It Works and When to Use It

Most bolts, screws, rivets and nuts in the world start life as a coil of wire, not a bar of steel. They are shaped at room temperature in a cold forming machine that squeezes the wire into a die, blow by blow, until a head, a collar or a shank appears. If you buy fasteners, or you need a special part made to your drawing, knowing how cold forming works tells you what is cheap to make, what is expensive, and what to ask your supplier before tooling starts.

This guide covers the process, the materials, the design rules that decide whether a part can be cold formed, and what to send when you want a quote for a custom cold formed fastener.

1. What Is Cold Forming?

Cold forming is a metal forming process in which wire or rod is pushed into shaped dies at room temperature, under very high pressure, until it takes the shape of the die. No material is cut away. The metal flows, like very stiff clay, into the space the tooling gives it.

You will see several names for the same family of processes:

• Cold heading: the original term, from forming the head of a bolt or rivet. Still the most common word in the fastener trade.
• Cold forging: often used for heavier or more complex parts, but in practice it means the same thing.
• Cold forming: the umbrella term, covering heading, extrusion, piercing and trimming done on the same machine.

The opposite is hot forging, where the steel is heated until it is soft enough to shape. Hot forging is used for very large diameters or shapes that cold metal cannot reach, but it gives rougher surfaces, looser tolerances and higher cost per part.

2. How the Cold Forming Process Works, Step by Step

1. Wire preparation. Coil wire is drawn to an exact diameter and, for medium carbon and alloy steels, spheroidise annealed so it is soft enough to form without cracking. A phosphate and lubricant coating is added so the metal slides in the dies.
2. Cut-off. The machine feeds the wire and shears a slug of the exact volume the finished part needs.
3. Heading and forming. The slug is transferred through a series of stations. Each blow upsets the head, extrudes the shank to a smaller diameter, pierces a hole, or forms a flange, socket or recess.
4. Trimming. Hex heads and similar shapes are often formed round and then trimmed to hex in the last station.
5. Thread rolling. Threads are rolled, not cut, between hardened dies. Rolling displaces metal instead of removing it, so the thread flanks keep a continuous grain flow.
6. Heat treatment. Bolts in property class 8.8, 10.9 and 12.9 are hardened and tempered after forming to reach the strength that ISO 898-1 requires. Low strength parts such as class 4.6 bolts or rivets usually skip this step.
7. Surface finish and inspection. Zinc plating, hot dip galvanising, zinc flake or other coatings are applied, followed by dimensional, thread and visual checks before packing.

The machines themselves are described by the number of dies and blows, for example a 2-die 3-blow header for simple bolts and screws, or a multi-station part former with four to six stations for flange bolts, stepped shafts and special parts. Depending on size and complexity, a header runs from dozens to a few hundred parts per minute.

3. Why Cold Formed Fasteners Are Stronger and Cheaper

Unbroken grain flow

In a machined bolt, the cutter slices through the grain lines of the bar at the underhead radius, which is exactly where a bolt carries the most stress. In a cold formed bolt, the grain follows the outline of the head and shank. Combined with work hardening from the forming itself, this gives better fatigue resistance at the head-to-shank junction and in rolled threads.

Almost no scrap

A machined part can turn a large share of the bar into chips. A cold formed part uses close to all of the wire that was cut off. On steel and especially on stainless, brass or copper, that material saving is often the biggest cost difference.

Speed and repeatability

Once the tooling is set, every part comes out of the same dies. Dimensions stay consistent across a long run, which matters for automatic assembly, collated screws and anything that goes into a tool magazine.

4. Cold Forming vs Machining vs Hot Forging

Many special fasteners use both: the blank is cold formed to near shape, and a secondary operation adds a cross hole, an undercut or a tight-tolerance diameter that forming cannot produce.

5. Materials Used for Cold Formed Fasteners

• Low carbon steel (such as SAE 1008 to 1022): rivets, class 4.6 and 4.8 bolts, self drilling and wood screws that are case hardened afterwards.
• Boron steel (such as 10B21 and 10B33): forms easily in the soft condition and hardens well, widely used for class 8.8 and 10.9 bolts and screws.
• Medium carbon and alloy steel (such as 1035, 1045, 4140 or SCM435): higher strength bolts after heat treatment; needs spheroidise annealing before forming.
• Stainless steel (cold heading grades such as 304HC, 316 and 302HQ): work hardens quickly, so it needs more forming force and more careful tooling than carbon steel.
• Brass, copper, aluminium and silicon bronze: electrical parts, decorative screws and architectural rivets.

6. Can Your Part Be Cold Formed? Design Rules to Check

These points decide whether a custom part can be made by cold forming alone, needs a secondary operation, or is better machined:

• Head volume. A large head on a thin shank means a lot of wire must be upset. As a rule of thumb, a length of about two to three wire diameters can be upset in one blow before it buckles; bigger heads need more blows or a larger starting wire that is then extruded down.
• Radii instead of sharp corners. Metal flows around radii. Sharp internal corners shorten die life and can cause folds or cracks.
• Features along the axis. Heads, collars, steps, sockets and recesses that line up with the axis of the part are natural for forming. Side holes, grooves and undercuts need a secondary operation.
• Length to diameter ratio. Very long, thin parts are fed and transferred with difficulty; check the maximum length your supplier’s machines can handle.
• Tolerances. Cold forming holds tight tolerances on heads and shanks, but a diameter or face that must be ground or turned should be marked clearly on the drawing.

A good supplier will look at your drawing and suggest small changes, such as a larger radius or a slightly different head height, that let the part be formed instead of machined. That is usually where the largest saving on a special fastener comes from.

7. Tooling and Order Quantity

Every cold formed part needs its own set of punches and dies. For standard sizes the tooling already exists. For a new special part, the tooling has to be designed and made first, and the setup time on the machine is the same whether the run is short or long. That is why cold forming becomes more attractive as quantity goes up, and why low volume specials are sometimes machined for the first batch and moved to cold forming once demand is proven.

8. Quality Checks for Cold Formed Parts

• First article check of every new tool setup against the drawing
• Visual checks for head cracks, folds and laps, especially on stainless and high strength steel
• Thread checks with go/no-go gauges after rolling
• Hardness and mechanical property tests after heat treatment for classes 8.8 and above
• Coating thickness and adhesion checks after finishing

9. What to Send When You Need a Custom Cold Formed Fastener

The more complete the first enquiry, the faster a supplier can tell you whether the part can be formed and what it will take:

• A drawing, or a sample, or clear photos with a ruler or caliper in view
• Material and strength grade, or the standard the part must meet (ISO, DIN, ASME or AS/NZS)
• Surface finish and any corrosion requirement
• Annual quantity and the size of the first order
• Where and how the part is used, so critical dimensions can be identified

10. Frequently Asked Questions

Is cold forging the same as cold forming?

In the fastener industry the terms are used for the same process: shaping wire at room temperature in dies. Cold heading is the older, more specific name for forming heads.

Are cold formed bolts stronger than machined bolts?

For the same material and heat treatment, yes in the places that matter most. The grain follows the head and thread profile instead of being cut, which improves fatigue performance at the underhead radius and in rolled threads.

Can stainless steel fasteners be cold formed?

Yes. Cold heading grades such as 304HC and 316 are used for stainless bolts, screws and rivets. They need more force and tighter process control than carbon steel because stainless work hardens quickly.

Which parts cannot be cold formed?

Parts with side holes, deep undercuts, very large heads on small shanks, or diameters beyond the capacity of available headers. These are either formed to near shape and finished by machining, hot forged, or machined from bar.

Working With Linkworld on Cold Formed Parts

Linkworld has more than 20 years of fastener export experience and runs its own cold forming workshop, working with partner factories for heat treatment and surface coating. Our own QC team checks dimensions, threads and packaging in our inspection room before shipment. We make both standard fasteners and custom fasteners made to drawing.

Have a part you would like to cold form?
Send your drawing, a sample photo or the specification through the enquiry form below, and our team will reply with the options that fit your project.